This invention relates to image intensifier tubes and more particularly to photoemissive cathodes for use in such tubes.
Image intensifier tubes multiply the amount of incident light they receive and thus provide an increase in light output which can be supplied either to a camera or directly to the eyes of a viewer. These devices are particularly useful for providing images from dark regions and have both industrial and military application. For example, these devices are used for enhancing the night vision of aviators, for photographing extraterrestrial bodies and for providing night vision to sufferers of retinitis pigmentosa (night Blindness).
Image intensifier tubes utilize a photoemissive wafer which is bonded to a glass faceplate to form a cathode. Light enters the faceplate and strikes the wafer, thereby causing a primary emission of electrons from the opposite surface.
In forming the photoemissive cathode, it has been found that during heat cleaning of the cathode after the photoemissive wafer is bonded to the faceplate, crosshatching marks and/or "brush lines" appear in the otherwise cosmetically uniform transparent cathode wafer. These marks destroy the usefulness of the cathode. They also occur at a point in the fabrication of the cathode at which considerable time, expense and materials have already been expended.